Leading Texas firm Baker & Botts is "evaluating" the legal marketplace in London with a view to opening an office in the capital.
It is understood the move was prompted by the firm's Moscow office, where Russian clients are keen to have access to Western markets.
Baker & Botts, a 394-lawyer commercial firm, has offices in Texas, New York, Washington and Moscow.
Partner Joel Swanson said: "We are evaluating the London market and the opportunities." He said the potential push into London was driven by a major client but he would not comment further.
One US management consultant described the Russian market as "incredibly active at the moment". He added that a move to London by Baker & Botts would be "a re-run" of Akin Gump Strauss Hauer & Feld, another large Houston firm with an active Moscow office, which opened a London office in April this year.
Last month New York practice Cadwalader Wickersham & Taft and Atlanta firm Paul Hastings Janofsky & Walker, announced they were opening London offices.